Vacuum tube



' I April 17, 1945. w E EL 2,373,949

VACUUM TUBE Filed Jan. 17, 1944 8 INVENTOR 1 WILL/AM M. E/ EL Ill- 5 8M6 ATTORNEY Patented Apr. 17, 1945 VACUUM TUBE William W. Eitel, San Bruno, Calif., assignor to Eitel-McCullough, Inc.,

San Bruno, Califl, a corporation of California 7 Application January 17, 1944, Serial No. 518,643 4 Claims. (Cl. 2 50 2'z.5

My invention relates to vacuum tube structure, and more particularly to improvements in the internal electrodes thereof.

When vacuum tubes are in certain kinds of service they are subjected to vibration and shock which is prone to cause breakage of fragile in ternal elements such as the filament. In tubes wherein the cathode and grid electrodes are free at one end, which type of structure has numerous advantages from the standpoint of manufacture, there is special danger of filament breakage due to relative vibration between the electrodes.

"ltis among the objects of my invention to provide a tube of the character described having an electrode construction designed to resist filament breakage.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention, as I may adopt variant embodiments thereof within the'scope of the claims.

Referring to the drawing:

Figure 1 is a fragmentary view, partly in section and partly in elevation, showing a tube embodying the improvement of my invention; and

Figure 2 is an enlarged top view of the grid and center rod.

Figure 3 is an enlarged fragmentary side view,

of the upper portions of the grid and filament structures, showing a modified arrangement.

In terms of broad inclusion, my tube comprises an envelope, a pair of concentric electrodes in.

the envelope each having an upper free end and a lower terminal end. One ofthese electrodes includes a fragile element such as a filament strand. Supporting means is provided in the envelope connected to the terminal ends of the elec trodes, and means .is provided adjacent the free ends of the electrodes to prevent contact of the fragile element with th other electrode upon vibration thereof.

In greater detail, and referring to Figures 1 and 2 of the drawing, my tube comprises an envelope 2 of vitreous material such as glass having a reentrant stem 3 with an exhaust tubulation 4. A pair of concentric electrodes includin a cathode 6 and grid 7 are provided in the envelope. The usual plate structure, which may be suspended from the upper portions of the envelope, .is not shown because my improvements are sufiiciently illustrated by the two electrodes shown.

The cathode has a center rod 8 sealed to stem 3. Filament wires 9 extend longitudinally of the center rod and are hairpin-shaped with the upper bights clamped between top disks ll. These disks are apertured to slide along rod 8. The lower terminal ends of the filaments are welded to supporting brackets l2 secured to the upper ends of leads l3 sealed to stem 3.

Connection to leads I3 is made through flexibleconductors I6 when the tube is based. A metallic shield l6 capping stem 3 protects the latter against heat and electron bombardment. Tension is applied to the filaments by a sleeve ll encircling center rod 8 and interposed between a top disk H and spring l8 which rests on a stop l9 secured to the rod.

Grid I is of the cage type having vertical bars reinforced by a wire spiral. The lower end of the grid terminates in a base ring 2| supported by a bracket 22 secured to a lead 23 sealed to the side of the envelope. The upper end of the grid is free as in the upper end of the cathode structure. This free-ended feature of th electrodes has many advantages, particularly in assembling the tube. The disadvantage however is; that the upper ends are subject of vibration when the tube is jarred. This is apt to cause breakage of the fragile filament when it hits the grid. Much filament breakage is traceable to this cause.

My solution to the problem is to provide means adjacent the free ends of the electrodes to prevent contact of the filament with the grid upon vibration thereof, This is accomplished inFigures 1 and 2 by projecting center rod 3 up through an aperture 24 in the top 26 of the grid, the spacing between the rod and rim of the aperture being less than the distance between the filament wires concentric electrodes in the envelope each having an upper free end and a lower terminal end, one of said electrodes including a fragile element, electrode supporting means in the envelope connected to said terminal ends, and means adjacent the free ends of the electrodes and normally spaced freely from at least one of said electrodes to prevent contact of said fragile element with the other-electrode upon vibration thereof.

2. A tube comprising an envelope, a cathode center rod having an upper free end and a lower end fixed to the envelope, a filament wire extending alongside the center rod and held at its upper end by said rod, a cathode lead projecting into the envelope and. connected to the lower end of said wire, avgrid mounted in the-envelope and disposed about the filament wire, and means coacting with the center rod and normally spaced freely from the grid to prevent contact. of .said filament wire with the grid upon vibration thereof.

3. A tube comprising an envelope, acathode said wire, a grid mounted in the envelope and disposed about the filament wire, and a top on the grid having an aperture through which the center rod projects, said rod being normally spaced freely from the rim of the aperture a distance less than the distance between said filament wire and the grid.

4. A ,tube comprising .an envelope, a cathode center rod-having an upper free end and a lower end fixed to the envelope, a filament wire extending alongside the center rod and held at its upper center rod having an upper free end and a lower end fixed to the envelope, a filament wire extending alongside the center rod and held at its upper end by said rod, a cathode lead projecting into the envelope and connected to the lower end of end by said rod, a cathode lead projecting into the-envelope and connected to the lower end of said wire, a grid -mounted in the envelope and .disposed:about.the filament wire, and a laterally projecting stop on the center rod within the space enclosed by the grid, said stop being spaced from thegrid a'distance less than that between the filament wire and the grid.

WILLIAM W. EITEL. 

